As higher definition and performance are demanded, modern mobile phones such as smart phones require a very high precision for providing output values (for example, a clock frequency, a grayscale voltage, etc.) of various circuits built in a display panel driver IC (Integrated Circuit). To this end, a trimming method has been conventionally used to achieve a high precision of the output values in a shipment test.
In more detail, the conventional trimming method performs the operations of (1) measuring a trimming-before output value for a trimming object circuit, (2) calculating a trimming value based on a result of the measurement with reference to a prepared unique trimming table, and (3) carrying out an actual trimming process, and (4) measuring a trimming-after output value.
FIG. 17 is a view showing an ideal trimming result. If a trimming circuit assembled into a trimming object circuit has no manufacture tolerance (manufacture tolerance of capacitors, resistors, switches and so on forming the trimming circuit), the earlier-described conventional trimming method can be used to adjust a trimming-after output value to a target value.
However, in some cases, the trimming-after value is deviated from the target value due to the manufacture tolerance of the trimming circuit.
FIG. 18 is a view showing a non-uniform trimming-after output value due to a manufacture tolerance of a trimming circuit. As shown in FIG. 18, even if a trimming-before output value is trimmed for the same sample using the same trimming value, a trimming-after output value may be varied if a trimming circuit has a manufacture tolerance.
The conventional trimming method does not consider the manufacture tolerance of the trimming circuit and accepts it as a margin of error even if the trimming-after output value is non-uniform. However, the manufacture tolerance of the trimming circuit cannot be ignored in order to realize the required high trimming precision.